1. Field of the Invention
This invention relates generally to a disk drive power management system for application to low-power computer systems and specifically to a powered-down mode sequencer that adapts to recent usage patterns.
2. Description of the Related Art
Recent improvements in computer hardware technology have led to computer systems wherein the disk drive data storage device consumes more power generally than other hardware elements such as the memory and microprocessor. It is generally desirable to reduce the power consumption of an inactive disk drive apparatus in some manner, such as by switching it to a state of reduced readiness that consumes less power than a fully functional disk drive state. Such practice also reduces the duty cycle for the disk drive apparatus, thereby improving service life and reliability. The recent popularity of battery-powered laptop computers and notebook computers has made disk drive power management even more important and desirable.
As used herein, the management of disk drive power consumption refers to Direct Access Storage Devices (DASDs) such as rigid magnetic disk drives as well as optical mass storage disk drives and other related apparatus. The problem of disk drive power management is also well-known in the digital imaging arts, including magnetic drives for digital imaging still cameras and portable video tape recording apparatus. These arts rely on small, portable recording devices powered by small, light batteries having low energy storage capacity. Thus, effective power management is crucial to the usefulness of such apparatus.
For instance, in U.S. Pat. No. 4,161,002, Isao Saito discloses a battery-operable tape recorder that reduces the rotary magnetic head drive power during the pause mode to reduce power consumption. In U.S. Pat. No. 4,717,968, Richard C. Painton et al. disclose a magnetic video disk player for the storage and reproduction of still photographs that is automatically cycled into a special quiescent state after a predetermined time interval elapses without user instructions. The disk drive spindle motor is stopped in the quiescent state to conserve power and reduce disk wear. In Japanese patent JP03-186073, Kazu Saito discloses an automatic power switch that shuts down a digital imaging recording and reproducing apparatus when no operation is performed during a first fixed time interval when a storage medium is present and during a second shorter fixed time interval when a recording medium is absent from the device. Other fixed-delay power supply circuit interrupters for battery-powered cameras are disclosed in U.S. Pat. Nos. 4,250,413 and 4,269,496.
The power management of floppy disk drives has been known for many years. For instance, in U.S. Pat. No. 4,376,293, Nobuyasu Teramura et al. disclose a magnetic disk device wherein the spindle driving circuit is automatically energized when the disk is mounted on the spindle and automatically de-energized after a predetermined time interval thereafter to ensure proper disk centering and optimal power consumption. In U.S. Pat. No. 4,635,145, Nobuyauki Horie et al. disclose a floppy disk drive system with a stand-by mode in which power is removed from the drive circuits for the head-positioning motor and spindle motors when no motor-activating signal is received during a predetermined time interval. Similar arrangements are disclosed in U.S. Pat. Nos. 4,684,864 and 4,783,706 as well as Japanese patents JP01-013253 and JP62-262265. All practitioners suggest fixed delay time intervals for powering-down functions.
Practitioners have also suggested many useful methods for power management in rigid disk drive systems such as DASD and the like. For instance, in U.S. Pat. No. 4,991,129, Jack S. Swartz discloses a dual mode actuator for disk drive applications in portable computers. Swartz teaches the use of a lower operating voltage and power when the system is battery-powered and a higher operating voltage and power when the system is powered by commercial electricity. In Japanese patent JP04-102261, Hisatoshi Katahara teaches a dual-mode rigid disk power-down technique where contact surface stiction (CSS) is avoided by keeping the head "floating" above the disk when the primary apparatus power is disabled during a low-power operating mode by occasionally "kicking" it to keep the disk turning. In Japanese patent JP02-306483, Eiji Chigusa teaches a two-valued delay time interval scheme where the head actuator motor only is powered-down after the elapse of a first time interval and the spindle drive system is powered-down after the elapse of a second longer time interval. Finally, in Japanese patent JP02-306483, Kazuo Kawasaki discloses a CSS and power control scheme wherein the head is moved to a landing zone and the spindle motor power is disconnected after elapse of a single fixed time interval following the previous disk access.
The usual practice in the art is now to stop the spindle motor and power-down most of the electronics shortly after completion of an operation in a floppy disk drive. Similarly, in rigid disk drives, it has become a standard practice in the art to offer one or two reduced power operative modes with associated fixed delay time intervals. For instance, a review of the Premier Technology LiteDrive (PC Magazine, vol. 6, no. 16, p. 244, Sep. 29, 1987) discloses the power management technique where the user specifies a fixed time delay interval for powering down the LiteDrive. M. Druffin et al. (IBM Technical Disclosure Bulletin, vol. 31, no. 1, pp. 485-7, June 1988) suggests a power-manager system in microcode for both rigid and floppy disk drives that powers-down the drive under microcode Control after a ten minute delay time interval without user access. R. C. Swartz (IBM Technical Disclosure Bulletin, vol. 29, no. 11, p. 4763, April 1987) suggests a low power standby mode that can be entered either by default after a fixed time interval or actively under program control. In U.S. Pat. No. 4,980,836, Robert R. Carter et al. disclose a power consumption control system for battery-powered computers that monitors the address bus to discover when selected peripheral devices have not been accessed for a preset delay time interval, powering-down the entire system and stopping the system clock to enter a standby mode after the preset delay time interval has elapsed. The Carter et al. system is awakened by depressing a standby switch rather than by requesting peripheral device access. Japanese patent JP63-224078 also discloses an interface circuit for entering a standby mode.
In U.S. Pat. No. 4,649,373, Patrick M. Bland et al. disclose a self-contained battery-powered keyboard entry device that uses a microprocessor to conserve power by automatically powering-down to a standby mode between keystrokes. In U.S. Pat. No. 4,933,785, James H. Morehouse et al. disclose a disk drive apparatus that includes hardware and software for reducing power consumption. Morehouse et al. suggest removing power from the drive control electronics after a predetermined delay time interval without an incoming disk access request. After an additional second predetermined delay time interval, the spindle motor power is next removed. By removing control electronics power before removing spindle motor power, Morehouse et al. acknowledge that more time is required to restore spindle speed following motor shutdown than to restore controller power. Unfortunately, the Morehouse et al. method is not optimal because a predetermined delay time interval following the most recent disk access is not a particularly useful indicator of the probability that another disk access request is imminent. Also, powering-down selected separately-powered components is not necessarily the best way to reduce disk drive power consumption because the capacity to quickly restore full disk operability is also an important user requirement.
Although portable computers could provide several control levels for finding a useful tradeoff between power consumption and performance, the first level in the art is still the human user, who may disable functions that are not needed and who can specify to the control program the degree of performance degradation acceptable in exchange for reducing power consumption. The next control level is the computer control program, which uses clock data, user inputs and default values to decide when to send shut-off and readiness mode commands to individual separately-powered components in the system. Finally, the separately-powered elements may each decide, from internal and external instructions, when to reduce power by going to a lower-power operating mode. However, in the art, the system and subsystem decisions to shift to lower levels of readiness are made solely in terms of a predetermined delay time interval since last use. Also, the powered-down operating mode for separately-powered elements is the "zero-power" operating mode and not a "reduced-power" operating mode.
Finding the best strategy for selecting from among several powered-down operating modes is usually seen as a problem that is separate and generally independent of finding the likelihood of an imminent new disk access request. However, coordinated solutions to both problems are necessary to optimize disk power consumption even though they present independent issues. For instance, both the microprocessor and the drive spindle motor could be operated at a reduced power to conserve energy while also offering rapid restoration to full power operation. The decision to operate at reduced power should consider the present likelihood that the host is engaged in activity that will soon result in a new disk access request. The method for establishing such likelihood is additional to the techniques for optimizing power-down mode sequences.
There is accordingly a clearly-felt need in the art for a system that can establish the optimal balance between reduced power consumption and immediate disk drive accessibility. Even those practitioners who suggest sophisticated multi-mode power-down schemes rely on fixed delay time intervals, whether predetermined or user-specified. Furthermore, the order of transition through several reduced-power operating modes is nonadaptive and predetermined according to all known power-management systems, none of which provide any means for adapting the power-down sequence or schedule to changes in the likelihood of an imminent command for disk access. These unresolved problems and deficiencies are clearly felt in the an and are solved by this invention in the manner described below.